1. Field of the Invention
The present invention relates generally to treatment of breathing disorders. In particular, the present invention relates to a nasal interface device that is relatively small, lightweight, easy to use, and can be connectable to a breathing apparatus.
2. Background of the Invention
Sleep-disordered breathing (“SDB”) includes all syndromes that pose breathing difficulties during sleep. These include obstructive sleep apnea (“OSA”), mixed sleep apnea (“MSA”), central sleep apnea (“CSA”), Cheyne-Stokes respiration (“CSR”), and others. Some form of SDB occurs in approximately 3-5% of the U.S. population.
Anatomical problems such as obesity or an abnormally narrow upper airway are known to cause obstructive forms of SDB, in which the airway is vulnerable to collapse as a result of fluid dynamic stresses imposed by breathing. These stresses produce collapse during sleep, especially during rapid-eye-movement (“REM”) sleep, when there is a reduction in the tone of muscles holding the airway open. An appropriate interface is required in order to deliver continuous positive airway pressure (“CPAP”) therapy, during which air pressure in the range of 4-25 cm H2O is delivered from a pressure generator, via delivery hosing, and through the interface in order to pressurize the airway so that it will resist such collapse. Various types of interfaces are known, including nasal masks covering and creating a seal with the skin surrounding the nose, oro-nasal masks covering and creating a seal with the skin surrounding the nose and mouth, and “nasal pillow” devices which directly engage the nares of the nose by inserting soft, expandable elastomer tubes just inside the entrance to the nostrils. Small leaks are acceptable in such devices, which in any case usually incorporate an exhalation orifice producing a fixed leak in the range of 30-50 liters per minute to provide bias flow for the pressure generator and to prevent rebreathing of exhaled gases.
Neurological difficulties in controlling levels of blood gases, such as carbon dioxide (“CO2”) and oxygen (“O2”), are increasingly being recognized as important contributors to other forms of SDB. This is especially true of the “central” syndromes, MSA, CSA and CSR, which may account for as much as 20% of all SDB. Changes in the neurological system that control blood gases often produce cyclic fluctuations in blood gases, and thus, unsteady respiratory patterns that cause arousals from sleep. These changes are accompanied by spikes in blood pressure and release of stress hormones that can cause long-term damage to a number of organ systems. Additionally, some SDB syndromes involve not only fluctuations in levels of blood gases, but also abnormal average levels of blood gases. For example, low levels of dissolved CO2 in arterial blood are frequently encountered in CSR, making the blood alkaline and posing a clinical problem. Therapies directed towards the central SDB syndromes may involve modulation of breathing gases or control of exhalation of carbon dioxide. These therapies are able to stabilize respiration and establish appropriate blood gas levels by restoring normal control of blood gases. When such therapies are in use, substantially leak-proof interfaces are required in order to permit careful control of the gases being exchanged between the therapy devices and the user. Leaks as small as one liter per minute, which would equate to the amount of flow that would pass through a hole as small as 1 millimeter in diameter, may negate the effects of the therapy. Thus, many conventional interface designs currently in use for delivery of CPAP therapy would not be suitable for use in treatment of the central SDB syndromes, and a much more secure interface design is needed for optimum therapy.
Respiratory interfaces typically provide gaseous substance(s) to a user in a variety of applications, including treatment of the above referenced illnesses, anesthesiology, and assistance in breathing.
Many respiratory therapies attempt to manage precisely the inhaled, mixed and exhaled gases for a user. This may be achieved through a tight seal between the interface and facial contours of the user. A tight seal may be necessary not only in order to provide precise control of gases exchanged with the user, but also to prevent escape of inhalational agents into ambient air where they may affect clinical personnel. For example, when a respiratory interface is utilized in treating complex sleep apnea, a closed system is required to control the amount of carbon dioxide that is exhaled by the user.
In the past, a tight seal has usually been achieved through the use of straps and harnesses to pull the interface tightly against the user's face. Since facial geometries vary, the amount of pressure applied to the skin by the interface will vary from place to place on the face, creating “hot spots” where pressure may be quite high. In some instances, the pressure may be high enough to prevent effective blood perfusion at the hot spots, causing long-term skin breakdown and damage to the face of the user. Therefore, it may be desirable to have an interface that conforms to a user's face and puts little or no positive pressure on the user's face while providing a sufficient seal.
The hoses and tubes associated with many respiratory therapies apply various torque forces to the interface, making it desirable for the interface to be sufficiently rigid or stiff to provide a stable physical platform to resist such forces, and to provide the user with the perception of security and stability of the interface and seal when in use. In the case of respiratory interfaces that create a seal by engaging the nares of the nose with nasal pillows, it is essential that the interface provide a geometrically stable platform to hold the nasal pillows securely in relationship to the nose, otherwise there is a risk that torque forces will cause one or both of the nasal pillows to disengage from the nare, creating a large air leak.
A competing concern to the rigidity of an interface is its ability to conform to user's individual facial features while providing comfort to the user. Compliance with continuous positive airway pressure therapy is reported to be less than 50% after one year, primarily as a result of interface discomfort. The ability of an interface to conform to a user's face comfortably is generally provided by a cushion. However, the cushion also serves to distribute forces applied to the interface such as pulling caused by the attached hoses and tubing, thereby limiting the degree of conformity with the face and the degree of comfort.
Further, conventional CPAP masks and other interface devices are bulky, heavy, and are difficult to operate. Thus, there is a need for a light-weight nasal interface device that can provide air-tight connection to a breathing apparatus and allow flexibility of movement to its user.